1. Field of the Invention
The present invention relates to a friction pair that has a friction member and a mating member. The friction member and the mating member generate a braking force owing to a friction force generated between them.
2. Description of the Related Art
Various performances have been demanded on a friction pair. For instance, one that is difficult to generate a vibration (judder) at the braking is in demand.
The judder is caused when a rotor (mating member) is subjected to an uneven wear. That is, as shown in FIG. 1, when the rotor rotates with wobbling largely in an axial direction at the time of high-speed running, the rotor contacts partially with the friction member at low surface pressure at the time of idle running, which is a non-braking time. Thus the rotor is partially ground and the uneven wear (DTV: Disc rotor Thickness Variation) is generated on the rotor. When the friction member is pressed against the rotor having a large DTV, a magnitude of the braking force wobbles and the judder occurs.
One method to suppress the judder is by reducing the aggressiveness of the friction member in relation to the rotor, thereby suppressing the occurrence of DTV. For instance, the friction member contains a raw material with a high aggressiveness, and an amount of the raw material is reduced. Or a soft raw material such as rubber is added to the friction member.
However, in the friction member where the raw material with a high aggressiveness is reduced, the friction coefficient becomes low and as a result a friction performance cannot be sufficiently satisfied.
In the friction member where rubber is added, the elastic force of the rubber disturbs the aggressiveness of the friction member. However, when the braking temperature becomes higher, the rubber is denatured. Accordingly, there is a problem in that, owing to the denaturing of the rubber, the performance of disturbing the aggressiveness against the rotor becomes incapable of maintaining and a decomposed material deteriorates the friction coefficient.
Various friction members are described in JP-A-6-346932, JP-A-7-26031 and JP-A-7-3247, yet none of these references provides a suitable solution for the suppression of the judder.
The friction member disclosed in JP-A-6-346932 includes 0.5 to 20% by weight of copper oxide powder. Thus the copper oxide powder may suppress noise, while securing the friction coefficient and the friction stability. Yet, this disclosure fails to teach, suggest or disclose a particle diameter of the copper oxide powder.
The friction member disclosed in JP-A-7-26031 includes powder of an ash layer reinforcing agent. Thus the powder may suppress an organic component from becoming ash and may prevent the friction member from disintegrating and disappearing. The powder is made of a raw material such as copper oxide and causes a sintering reaction in an ashing temperature region to strongly bond an ash component. Yet, this disclosure discloses a prefered amount of copper oxide to be 10 to 20% by volume.
The friction member disclosed in JP-A-7-3247 includes a copper compound such as copper oxide. Thus the copper compound may improve a balance between the mechanical strength and the friction characteristics. The copper compound has an average particle diameter in the range of several to several tens μm and an addition amount thereof is in the range of 1 to 10% by volume.
However, the above three types of friction member are neither developed for suppressing the judder nor suitable for suppressing the judder. Furthermore, in the friction member involving JP-A-7-26031, there is a problem in that the amount of copper oxide by volume, as disclosed, retracts from the moldability and thus manufacturability of the end product.
Thus, there is need in the art for a friction pair, in which a friction pair is able to suppress the judder stably and a friction member is able to be molded excellently.